The present invention relates to an electrophotographic apparatus.
An electrophotographic apparatus for copying both a sheet document and a thick document such as books or the like has variously been developed. As an example, there is an apparatus provided with the so-called sheet feed device for feeding a sheet document by means of a roller or the like and a platen for thick document such as books on a movable document table, wherein the table is displaced to various positions, a stationary optical system is co-used, the document is moved in case of a sheet document and the table is moved in case of a thick document to expose and scan the document, and a copy is obtained. There are another apparatuses such that a sheet feed device is used as a main body to expose and scan the document by moving a platen plate on which a thick document is placed with the aid of a document feed mechanism, and an apparatus provided with an auto document feed device for automatically feeding sheet document.
Such prior electrophotographic apparatuses are to improve efficiency of sheet document copying on the same platen regardless of its construction. That is, the fundamental idea lies in that time loss of the reciprocatory action of a document table or scanning optical system is eliminated by successively scanning document by a sheet feed device. In this kind of devices, therefore, when each copy is obtained from a number of sheet documents, the document can quickly and advantageously be set. However, when a plurality (n) of copies are obtained from a number (m) of documents, it is necessary to expose and scan one document n times, so that the document should be fed m.times.n times. This is very inefficient and disadvantageous as compared with the device for repeating n exposing and scanning steps to only one document for m sheets by moving the optical system. When automatic setting is desired, 1-m sheets of copies are stacked for n times, which is also inconvenient. In case of copying a thick document such as book or the like, if n sheets of copies are obtained from one page, a next page cannot be put on the exposing and scanning surface until at least n sheets of copies are finished. In case of obtaining n sheets of copies from a number of pages, the time loss becomes considerably large for turning pages and setting document. Further, the device for moving a thick document platen with the aid of a document feeding mechanism in the sheet feed device is troublesome in operation and cannot be used for thick document in practice. The reciprocal step of an exposing and scanning system is carried out every time when the thick document is copied, so that this time loss cannot be avoided.
That is, in the prior electrophotographic apparatus for both sheet document and thick document, inefficient sheet document copying work has been improved by providing a sheet feed device for saving time loss caused by reciprocal movement of the exposing and scanning steps in sheet document copying, but new defects have been caused as described above, and particularly, the thick document copying work is still the same or rather troublesome in a certain kind of such devices.
On the other hand, there have been proposed various electrophotographic methods for obtaining a plurality of copies from an image-like modulating information formed by one exposure and scanning in these years. For instance, there is a method for obtaining a plurality of copies by forming an electrostatic latent image by uniformly charging, exposing and scanning an electrophotographic sensitive plate, developing the electrostatic latent image into a toner image, transferring the toner image to a recording paper without breaking the electrostatic latent image and thereafter repeating development and transfer.